X-ray image acquisition devices have been developed for various clinical applications. By emitting X-rays from an X-ray source towards an object to be examined such as for example a part of a patient and detecting the partially transmitted X-rays on the opposite side of the object, an image of the object showing its interior structure may be acquired due to the differing X-ray absorption properties for example of different types of patient tissue such as bones, muscles, etc.
For example, C-arm systems have been developed which comprise an X-ray source on one end of the C-arm and an X-ray detector on an opposite end of the C-arm. The C-arm may be moved in different directions, in translation direction and/or rotational direction, such that images of the object may be acquired in a large variety of orientations.
In one specific application, a plurality of two-dimensional X-ray images may be acquired under various observation angles and a three-dimensional image may be reconstructed from such plurality of two-dimensional X-ray images. Such three-dimensional image may help for example to visualize a region of interest of a patient to a physician. The three-dimensional image may be displayed to the physician in a screen in different orientations or in different slices. For example, displaying such three-dimensional image may help the physicist during an invasive surgery procedure. During such surgery procedure, additional X-ray images may be acquired and may be compared or overlaid to X-ray images acquired prior to the intervention.
For many clinical applications, it may be important to know the spatial relation between the region of interest within the patient and the acquired X-ray image. For example, in order to be able to easily compare X-ray images acquired prior to an intervention with X-ray images acquired during the intervention, it may be necessary to acquire both types of images at a same position and under a same orientation of the X-ray acquisition device with respect to the region of interest.
One possible application of X-ray imaging during surgery interventions is 3D roadmapping. Therein, a life 2D fluoroscopic image and a 3D reconstruction may be fused into a single visualization. An orientation, position and perspective of 3D data may be matched to a current pose of a C-arm system such that the content of the 2D data and the 3D data overlap. This technique may help to save contrast medium since the 3D reconstructed already shows a vessel volume within a region of interest in the patient. Further, it may increase confidence during the procedure, especially for complex vascular structures where the 3D image clearly shows the vascular morphology.
In order to be able not only to move the X-ray acquisition device such as the C-arm system with respect to a patient but also to be able to move the patient himself for example during a surgery procedure, patient tables have developed which comprise a table plate on which the patient may be stored and which table plate may be moved with respect to a table base fixedly standing on a floor. Advantageously, such patient tables comprise actuators which may be controlled to actively move the table plate with respect to the table base. For example, the table plate may be translated, rotated or tilted with respect to the table base. In order to allow such various movements, the table plate may be connected to the table base via at least one movable joint.
Advantageously, the patient table is adapted to detect an actual position of the table plate by acquiring position data of the at least one movable joint. For example, a position or an angle of a hinge or bearing included in the joint may be measured and the actual position and/or orientation of the table plate may be derived from such position data. Of course, the patient table may comprise more than one movable joint and the position data may be derived from a plurality of measured position values and/or angle values.
Automatic position control systems have been developed allowing storing and recalling a pose of a geometrical arrangement. It is available for both, the C-arm and the patient table geometry. Conventionally, this may be done by storing a mechanical position of the one or more joint(s) included in the C-arm system and the patient table, respectively.
However, it has been observed that using conventional automatic position control systems may not always result in satisfying positioning results.